Fuel cells combine oxygen and fuel to chemically generate electricity without combustion. Solid Oxide Fuel Cells (SOFC's) use ceramic materials as an electrolyte, typically a solid yttria-stabilized zirconium oxide (YSZ), which is an excellent conductor of oxygen ions at high temperatures. SOFC technology has the distinct advantage over competing fuel cell technologies (e.g. molten carbonate, polymer electrolyte, phosphoric acid and alkali) because of its ability to use fuels other than hydrogen and their relative insensitivity to CO, which act as poisons to other fuel cell types, but is a fuel for these cells. The general design of a SOFC is two porous electrodes separated by a ceramic electrolyte. The oxygen source, typically air, contacts the cathode, for example strontium doped lanthanum manganese oxide (LSM), strontium doped lanthanum cobalt iron oxide (LSCF), or other conventional cathode material, to form oxygen ions upon reduction by electrons at the cathode/electrolyte/oxygen triple phase boundary. The oxygen ions diffuse through the electrolyte material to the anode where the oxygen ions encounter the fuel at the anode forming, water, carbon dioxide (with hydrocarbon fuels), heat, and electrons. The electrons transport from the anode through an external circuit to the cathode. A particularly useful anode for many cells is a liquid tin anode.
A Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC) is a fuel cell that combines the efficiency and reliability of conventional SOFCs while expanding the range of fuels that can be used, including gaseous, liquid, and solid fuels, and is particularly tolerant to impurities, such as sulfur. Another advantage is that coking is not a problem due to the low catalytic activity of tin toward carbon depositions and because the tin is a low vapor pressure liquid at use temperatures, for example, above 232° C., such that a stable surface to promote excessive coke formation is not available. Typically the tin is supported on the YSZ electrolyte, which is relatively thick.
Because of the thickness of the electrolyte, available LTA-SOFCs, which are used at temperatures in excess of 1000° C. have power densities that are significantly lower than other state of the art SOFCs, including those designed to function at lower temperatures, see for example International Application Publication No. WO/2010/045329. Hence, a SOFC that combines a molten metal anode with a thin electrolyte to significantly lower the cells resistance is desirable.